A diffusion-kinetic model for predicting solder/conductor interactions in high density interconnections

A combined thermodynamic and diffusion-kinetic approach is very viable for developing microjoining and interconnection materials and processes, in particular, whenever thinner metallizations, coated overlayers, or smaller solder-joint volumes are encountered in very high density electronics. A diffusion-kinetic model based on the utilization of integrated diffusion coefficients and mobilities is introduced and discussed for calculating the layer growth of intermetallic compounds between metal conductors and tin-based solders and is exemplified with a relatively simple ternary Cu/SnBi system. The model has also been used for calculating the local nominal composition of the effective joint or contact region. Moreover, the mobilities of Sn and Cu in Cu6Sn5 and Cu3Sn intermetallic compounds are determined, and the role of both stable and metastable phase diagrams is discussed in predicting the appearance of possible reaction products as well as the driving forces for the dissolution, diffusion, and precipitation processes

High-temperature nitridation of Ni-Cr alloys

The nitriding behavior of nickel-chromium alloys was investigated at 1398 K over the range 1 to 6000 bar of external nitrogen pressure. The morphology of the nitrided zone depends on the concentration of chromium in the initial alloy and the N2 pressure (fugacity) applied upon the system. The transition from CrN to Cr2N precipitation was observed within the reaction zone after nitriding at 100 to 6000 bar of N2 when the chromium content in the initial alloys was 28.0 at. pct or higher. It is shown that the ternary phase p (Cr10Ni7N3) is formed in this system at 1273 K. through a peritectoid reaction between Cr2N and nickel solid solution and becomes unstable above 1373 K. The thermodynamic evaluation of the Ni-Cr-N system was performed and phase equilibria calculated. Evidence for "up hill" diffusion of nitrogen near the reaction front during the internal nitridation of Ni-Cr alloys at 1398 K was found. It was attributed to the relative instability of chromium nitrides and strong Cr-N interaction in the matrix of the Ni-based solid solution within the nitrided zone